Monday, April 16, 2018

Viscous DT on Blue Ridge Special Rubber Model

For a long time I have had this idea about installing a viscous DT (dethermalizer) system on a sport rubber powered free flight model. My first experiment installing a DT system was to install a fuse on a Guillow’s Lancer. This worked well and gave me experience handling a fuse but I wanted to try a viscous system because I wanted a system kids could use without playing with fire. Presently I am writing a couple of articles on viscous DT systems so this would be a good time to try a system on a smaller airplane.

Previously I had built a Blue Ridge Special from plans but lost it this winter on a frozen lake, I had the Volare two plane short kit so decided to build one and install a tiny rotary damper system using the E2 style rotary damper, the price is under $3. To keep the weight of the airplane as light as possible I used really light wood, which the instructions caution against. The leading edge started to bow in but I warped it straight, the problem came back when I covered the plane with Esaki tissue. All the covering was ripped off and laminated a piece of 1/16” square to the leading edge. Recovering went better except now the trailing edge was too soft. When I build the second model I think a light plastic will be used.

To make a timer I referred to Manuel Cisneros article; you remove a plastic gear, slip a tube over the shaft, and place a pin through the shaft. My particular rotary damper appeared to take more force to turn it so I slipped another plastic tube over the first tube to increase the torque. On this same model rotary damper on a glider it turned fine without the extra tube. The rotary damper was mounted on top of the fuselage because I was afraid it might interfere with the rubber motor if mounted on the side. Instead of popping up the rear of the stabilizer I decided to pop up the front of the wing. 

Coming Down from DT 

Recently I purchased a couple of small needle nose pliers with rounded jaws, this tool works good for bending wire in nice looking loops. All the wire used was from a common straight pin. The hinge in the rear of the wing would have a good deal of stress on it so I used a small strip of fiberglass cloth over it. Two sides of 1/16” balsa were used to make a small pylon, a short length of 1/8” square balsa under center of the wing in front slides into the groove between the two pylon sides. This should keep the wing from shifting in flight. A toothpick made a good peg for the DT line to wrap around. 

Everything appears to work fine on the ground, waiting for better weather for test flights. The weight of the plane without rubber was 11 grams, the rotary damper only weigh 3/10 of a gram. When I am happy with how this works I will build the other kit and do a better job of covering the wing.

Bill Kuhl

Related Links    Volare Short-kit 2 Pack  First Blue Ridge rotary damper used  Manuel Cisneros article on rotary dampers Fuse on Lancer video of Lancer flying and fuse DT

Friday, March 23, 2018

New Gollywock Build Report

What fun would it be if I did everything the same? At least that is my excuse for trying a new covering method and new DT system on my build of a New Gollywock this winter. Building another larger rubber model the Wilbur the previous winter, taught me much about building a rubber model larger than a p30. Again I ordered a prop blank from Volare and I knew what I needed for prop assembly hardware. Several people have suggested that I should try the tissue over mylar covering method, this time I gave in. I also ordered the Will Hubin electronic timer for this plane.

New Gollywock

Gliding from Small Hill

Along with the Jim O’Reilly plans I had ordered the Bob Holman laser-cut ribs for this plane. Construction was easier than the Wilbur that had the angled cross members in the fuselage. Covering with mylar I had done once before in building the Polecat X p30. What I wasn’t paying attention to when I ordered more ¼ mil mylar was that it was silver in color. The bottom of the wing was covered with clear mylar but then I had to use the silver mylar for the top of the wing. No doubt the silver is slightly heavier. 

Clear Mylar

Silver Mylar

When shrinking the mylar I got a little too much heat on it with the heat gun and it started turning brown in a couple of spots but never burned through. I tried to cover this up with the tissue colors that went over the mylar. Doping the tissue over the mylar I do not think I followed the proper procedure which is to use thinner to soften up the nitrate dope surface and attach the tissue. I attached it by brushing in the nitrate dope into wet tissue. Most places it worked fairly well but other spots mainly one fuselage side, there are spots that the tissue sags. I left the tissue off the upper side of the wing tips to save weight and try the silver-look.  On the fuselage I sprayed Design Master Floral paint over the orange tissue because it did not look good with the silver base. The fin was covered with silkspan and painted white for visibility. 

Mylar on Fuselage

From a few feet away the plane looked fine. The structures feel very rigid and the weight seems to be similar to other Gollywocks. Where I did add a little more weight was the installation of the Will Hubin electronic timer. Weight of the timer is around 3 grams, I found a servo with a case that weighs 1.8 grams, there is the weight of connectors and a 30 ma battery so total weight is around 7 grams. With this electronic timer you have to do the wiring but that makes it flexible as to what can be done. There is a programming box that is needed to create and download a program into the timer. The big positive is you can program to the second when the model will DT.

Will Hubin Electronic Timer

Programming Box and Testing Setup

So far the model has been test glided without the rubber from a small hill which looked straight ahead and a few real short power flights with a rubber motor and 40 turns. Adding rubber did change the CG but then I noticed the wing was sliding ahead with no stop on it, this has been corrected. With power it appeared the model would climb rather steep and go left. I am going to add the recommended thrust adjustments before more test flights.

Bill Kuhl

Related Vendor Links  Hubin Timers at Retro RC  New Gollywock – Volare Products prop blanks

Friday, March 16, 2018

Spring Flying and My New Stuff

Last weekend I was still cross country skiing and flying model airplanes over the snow but this weekend looks to be snow-free and low wind. There is still much I want to do as far as building new models, the last part of projects always seem to take the longest. For quick builds I had built a couple of small catapult gliders from J&H Aerospace and have been test flying over snow and this week grass. Small gliders take tiny adjustments to get flying well, I am learning. The gliders I built are the Aleda and Carbonette 8.  I did get in some test glides of the New Gollywock I built from O’Reilly plans, glide looks good, time to braid a rubber motor.

Extreme Closeup of Rotary Damper for Building DT
Close-up of Plastic Clock for building DT
Carbonette 8 Catapult Glider

New Gollywock Test Glide

My home computer was getting really old so I purchased a new Dell pc that is really tiny but powerful. I want to make more videos and a computer cannot be too fast for that. I am learning the Corel Ultimate video software which is similar to what I have used but yet different. For more electronic toys I purchased two different USB microscopes. The first one seems to only focus really close but the next one I purchased will focus farther away.  As I am working on an article on viscous DT timers I took many close-up pictures of rotary dampers and springs. On researching viscous DT I found many people build timers for rubber powered free flight model using what Hank Nystrom calls a “plastic clock” and other people refer to as Tomy Timers. Someone sent me a sample with the pendulum made from a quilting pin, with the spare pin they sent I created my own and it runs really well.

Timer Sample and One to Build From

As an investment in my model building I have purchased several items. For my health in the airbrush painting I am doing I purchased a respirator mask. For bending music wire I purchased a small needle nose pliers and a new wire cutter with longer handles. After so much use the old wire cutters become just about worthless. 

For Spray Painting

Witch Hawk 500 Stab

BMJR Streak

My first large glow powered free flight the Witch Hawk 500 is coming along well. The wing and stab were covered with Polyspan and then I used the dye Larry Davidson sells. It went on better than I thought it would. To finish the Flying Aces Moth rubber model I have to build a freewheel device and install the DT. One of the two ½ A NOS models I am building requires just the DT installed and another is ready for covering.

Related Links  Witch Hawk 500, Streak, and Smarty kits  - Polyspan & Dye  Aleda and Carbonette catapult gliders  New Gollywock  - Plastic Clocks  Corel Video editing software

Friday, February 23, 2018

Bad Experiment in Viscous DT Timer

Often when things do not go as planned; studying the reasons why can lead to a great learning experience. Example, one of the cheapest and lightest weight devices to bring down a free flight model airplane (DT or dethermalize) in a specified time before flying away is with a “viscous timer”. Basically a “rotary damper”, a device that slows down rotary motion is pulled by a “tension spring”. When a line with a loop that goes around and an arm comes off; either the stabilizer or the wing of the model plane moves upward causing the airplane to come down. There will be free flight modelers that think this method works pretty well and others that will avoid using this method completely.

Free Flight Discus Launch in DT Mode

Ikara Viscous DT TImer on P30 Model

Living in a cold climate I try to keep busy with my model airplanes even when I cannot fly outside, this winter I decided to review how all of my DT devices operated and time the length of a cycle until it dt’s. Other DT devices I have are electronic, mechanical with wound spring, and a burning fuse, the first two types are accurate but can be more expensive and heavier. What I was doing was like a science experiment and I realized in actual operation outdoors conditions would be different; mainly the temperature in my house is constant.

Badge Timer on Test Board

First I started with a P30 rubber model that had the Ikara brand viscous installed, running cycles of the timer continuously while watching TV; I recorded the DT times on paper. In looking at the data of the times over a couple of days there was one pattern I noticed of the first run normally took the longest and then the times were a little more consistent. This prompted questions to online model forums and I learned that this can be a characteristic of the fluid in the rotary damper, a couple of suggestions I received were to not move the rotary damper too fast and to work it a couple times before using the timer for a flight. 

Volare Spring Winder

In my experiments I tried two more viscous timers and also constructed my own springs with a winding device I purchased from Volare. I asked so many questions on model forums I am sure people are tired of me asking about viscous timers. In that in some ways this is like a mousetrap car in the use of a spring and the concept of leverage I consulted with Doc Fizzix the mousetrap car expert. I also searched Internet for any article related to this type of timer.

My plan is to write two type of articles with what I am learning, one for free flight modelers that I will submit to Free Flight Digest and another that is more about the science of how this seemly simple device functions. My hope is also to show students how to install in a fairly simple rubber powered airplane such as a Peck Sky Bunny.

About the bad experiment, what I found was that my operating the timer constantly with no break in between was causing my data of recorded times to be really inconsistent. After realizing that I waited several minutes before running the timer again. This is consistent with actual use in a model plane as it will normally take a few minutes to retrieve the model before flying it again. Now I was recording times that were consistent, I will write about why this is in future articles.

Bill Kuhl

Related Links  - Manuel Cisneros article on Viscous DT  Doc Fizzix Mousetrap Cars  - spring winding device  - National Free Flight Society 

Monday, February 5, 2018

Catching Up in February

I have not posted anything in a couple of weeks, so time for an update. The best news came in an email I received from a student I had helped online build model airplanes for the Wright Capacitor event in Science Olympiad several years ago. I have to give her much of the credit for asking good questions and being so responsive by email. She was thrilled to receive 6th place out of 61 teams at the national competition and decided to pursue aerospace engineering in college and has an internship lined up at Boeing this summer.

Witch Hawk 500

Wright Capacitor Model

This winter I have been busy building another fleet of free flight model airplanes, the building went pretty fast but finishing up all the ending details has not gone as fast. Of course I had to try some new things; one was the tissue over mylar covering technique on the New Gollywock rubber model I am building. I had covered with mylar once before and that went pretty well but I must have not applied the dope as consistent as needed to attach the tissue. Some places look real good, other spot have some sagging tissue, from a few feet away it looks fine and the finished structure is rigid and light.

New Gollywock

After building and flying my first glow powered model in several years last year the Basic Yeller powered by a Cox PeeWee .020 I decided to try more glow models again. I started building my largest free flight yet, the Witch Hawk 500 to be powered by a K&B .19. This is my first model with a mechanical timer for motor cutoff and DT, the timer is a Texas Timers MaxIIIA. I wanted to do everything by the book, so used the mounting kit and the plastic dust cover. Covering is Polyspan on surfaces and silkspan on the fuselage.

Basic Yeller
1/2A Streak Free Flight

Two smaller glow models are under construction also; these are the ½ A 2018 One Design models at the Nats, Streak and Smarty. BMJR had a sale on the two kits so I purchased both. The Streak is covered now but still needs to have clear dope and some trim, Smarty is in final construction stage.  I have purchased airbrush equipment but still waiting for the pressure regulator to arrive. There are plenty of Youtube videos on spray painting that I have been watching before experimenting with the equipment.

Flying Aces Moth

Another rubber power model kit that I am finally building is the Peck kit of the Flying Aces Moth. I also have the Volare short-kit that I might build with any improvements I see are needed. Instead of the included plastic propeller I purchased a prop blank from Volare, the wood propeller is almost half the weight of the plastic propeller. This model will have a viscous DT, I used Manuel Cisneros article on Rotary Damper Timers as a guide for setting up a DT system for this plane.

Icon A5 Electric RC

Flash X18 on Frozen Lake Winona
When the temperature and wind are not too bad I have been doing some winter flying both RC electric and some simpler free flight models. The frozen lake close to where I live gives a huge unobstructed flying site but so far there has been little snow for cushion when the model lands. Crashing on ice is about like crashing on concrete. When there was a little snow I had fun doing touch and go’s with the Icon A5 park flyer electric RC. I have been test flying the Flash X18 rubber powered free flight that Dick Bertrand uses in his Free Flight Rescue program. With some minor tweaks I am getting more consistent flights.

Bill Kuhl

Related Links

Thursday, January 11, 2018

Lost Blue Ridge Special on Ice

I should have known better, when a free flight model has a dark background behind it, losing sight of it is very easy. After two weeks of really cold weather, the lake close to my house was really frozen over hard; many vehicles and fish houses now dotted the lake. It warmed up last Sunday and I flew simple rubber powered models from the lake in weather that was slightly above freezing. Before it again turned really cold I wanted to get out on the lake again and took a day of vacation.

Blue Ridge Special on Ice

Forecast for the wind was to be more to the South which I thought the bluff would block but it appeared to be more out of North but it was switching around too, from the North drifted model towards the bluff. On a dark day with bare trees in the background it was easier to lose sight of a model. I had some flights on the Flash X18 but the last flight it did not transition well and came back hard to the ice breaking the plastic propeller hanger.  I then started flying the Blue Ridge Special built from plans a few years ago. Not very smart on my part I covered the model in green and yellow tissue which is hard to see in the grass but not so much in the snow.

Flash X 18

After a couple of flights where it landed fairly close I cranked in a few more turns and it started circling towards the bluff. Big mistake on my part I took my eyes off it for a couple of seconds while I reached down to pick up the other model. When I looked up, panic set in as I could not see the model flying again. I started walking towards where I had last seen it, now I just could not find it on the lake which was a combination of black and white because much of the snow had melted off.

AMA Maxi Jr

After about a half hour of looking, I decided to go home to get my binoculars and grab another airplane. When I came back I looked from the opposite bank and could spot a clump of leaves near the opposite shoreline but no sign of the model. Walking out half way, I launched my AMA Maxi Jr model and watched how it drifted. It drifted in at least a couple of directions during the flight, it appeared it was encountering some lift at times.

Blue Ridge 2 Pack

With the binoculars I continued searching the frozen surface, having never seen the model land is a bad thing. Maybe it did find a thermal and fly away, or maybe it went scooting across the ice in the gusty wind. After another hour of looking I gave up the search. Recently I had purchased the Blue Ridge Special short-kit 2-pack from Volare; I should just build two new models.

Bill Kuhl

Related Links  - Volare Products 

Friday, January 5, 2018

Cool Start for 2018 - Model Building

Most years I fly some type of model airplane on New Years day but not this year, just before the real cold that came on Christmas I had been flying my Icon A5 electric RC amphibian from the snow and a couple of rubber powered foam free flights, when the temperature got below 20 degrees F, I spent time building planes for 2018. In my last blog post I shared some pictures of what I am working on, those planes are farther along but you cannot see much change. Funny how those last details can take so long. 

Flash X18

Icon A5 from 2016 Picture
I did build a simple catapult glider during part of one evening, the Rookie from Stevens AeroModel. Everything included, even catapult rubber and stick, pennies for balance.  I also have the Hand Launch Glider With Dethermalizer kit from Stevens Aeromodel to build yet.  Arriving yesterday were a couple of more catapult glider kits from J&H Aerospace, no time for photo yet.  I had also received a sample kit of Flash X18 rubber power model a classic design of Frank Zaic and that built quickly, too bad it is so cold for testing.

Rookie Kit

Tubes used to Key Fuselage Pieces
Rokkie Complete

Trying a new to me electronic DT timer from Will Hubin FM-10.  I connected it up and tested with a servo I had on the bench and it worked fine. There is an external box that you program with and then download to the timer. I found a really small servo that weighs 1.8 grams that I plan to use with the timer in a rubber powered model, total weight is 7.92 grams. Rather heavy for this model but it should be 100% accurate.

Ready to Fly Weight

Programming Box in Rear for Timer

I had also purchased a wire winder to create my own tension springs from Volare Products. Some evening soon I will try to create some springs.

Bill Kuhl